1. Field of the Invention
The present invention relates to a method of manufacturing a housing or casing for an electronic apparatus such as a personal computer and the like, and more particularly relates to a method of manufacturing a casing for an electronic apparatus in which the formability, mechanical strength and heat radiating (or cooling) property are improved when metal and resin are integrated into one body by applying an adhesive agent of heat-resistant rubber or an adhesive agent of hot-melt and also by applying a film-like adhesive agent or a surface processing agent.
There is provided a method referred to as "in-mold forming" in which metallic parts and resin are integrated by means of injection molding. According to the in-mold forming method, metallic parts are set in a metallic mold, and then resin is injected into the metallic mold so as to integrate the parts with the resin. There are two types of in-mold forming methods, one is an insert forming method by which the metallic parts are embedded in the resin, and the other is an outset forming method by which resin parts are formed on a metallic base plate.
2. Related Art
Conventionally, for the casing for a portable electronic apparatus such as a notebook type computer, electronic notebook, portable telephone and the like, resin is used from the viewpoints of reducing the weight, improving the appearance, and maintaining the insulation. Usually, the weight of the casing is 30 to 50% of the entire electronic apparatus. Accordingly, when the weight of the casing is reduced, the weight of the entire electronic apparatus can be greatly reduced. In order to reduce the weight of the electronic apparatus, the wall thickness of the casing is reduced. However, the mechanical strength of the ABS (acrylonitrile-butadien-stytrene) resin, which is commonly used for the casing, is not sufficient, so that the wall thickness cannot be reduced. Therefore, the casings can be made of engineering plastics of high mechanical strength such as aromatic polyamide and PPS (polypropylene styrene) or can be made of polymer alloy of ABS-PC (polycarbonate) and can be made by adding a bulking agent such as carbon fiber.
However, compared with ABS resin, it is difficult to inject the above engineering plastics with sufficient pressure to form a thin wall. Further, it is difficult to coat or plate with metal the surface of the above engineering plastics. Furthermore, even when the above engineering plastics are used, sufficient mechanical strength and rigidity are not provided. Even when a polymer alloy is used or a bulking agent such as carbon fiber is added, the circumstances are the same. Especially, there is a probability that a portable electronic apparatus such as a computer or word processor be dropped while an operator is walking. Therefore, an anti-shock property is required for the casing so that not only the casing but also the inside electronic parts are not damaged even when the electronic apparatus drops from a height of approximately 1 m. In computer and other devices, the IC chips are highly integrated in accordance with the high processing speed of the apparatus. Therefore, the thermal output of the electronic elements is high. When these parts are substantially assembled into the casing at a high density, it is important to improve the heat radiating property. However, at present, a resin for forming a thin wall of high mechanical strength completely satisfying these properties is not provided, and a casing made of the resin is not provided, either.
On the other hand, in order to satisfy the required performance, there is provided a method of making a casing for metal such as an Al (aluminum) sheet, Al alloy, or of die-cast Hg (magnesium) alloy. However, in the case where the casing is made by means of aluminum sheet metal, it is difficult to form a boss, rib and engaging portion. In the case where the casing is made by means of aluminum alloy die-cast, it is difficult to form a thin wall not more than 1 mm. In addition to the above disadvantages, when the casing is made of these metals, the rigidity becomes high, so that a shock can not be absorbed when the apparatus drops onto a floor. In this case, there is a possibility that the intended electronic parts to protect are damaged although the casing is not damaged.
As described above, a single metal structure or a single resin construction does not offer the required mechanical strength, formability, anti-shock and heat-radiating characteristics.
However, when a resin and metal are combined the above problems can be solved. In order to integrate metal and resin into one body, there is provided a method referred to as an in-mold forming method. In-mold forming is applied to the casing in the following manner:
In one method, a casing is provided, in which a metallic net having electromagnetic shielding properties, the profile of which is the same as that of the casing, is subjected to insert forming, so that the electromagnetic shielding properties can be improved (Japanese Unexamined Patent Publication (Kokai) No. 59-124193: Electronic Apparatus Casing). In another method, a casing is provided, in which a metallic shielding case is integrally formed so that the number of processes for making the casing can be reduced and the mechanical strength can be improved (Japanese Unexamined Patent Publication (Kokai) No. 1-198099: Electronic Apparatus Casing). In still another method, a parabola aerial or antenna is provided, which is formed by means of in-mold forming (Japanese Unexamined Patent Publication (Kokai) No. 4-137804: Parabola Aerial and Manufacturing Method thereof). According to the former two methods, it is possible to improve the electromagnetic shielding property of the casing, however, consideration is not given at all to the mechanical strength, formability, anti-shock, and heat-radiating characteristics. Therefore, the above requirements cannot be completely satisfied.
In the in-mold forming method, metallic parts adhere to the formed resin when an anchor effect is used. When the end portions of the metallic parts are embedded in the resin, the resin layer holds the metallic parts, and when though-holes are formed in the metallic parts, the resin flows into the through-holes, so that an anchor effect can be provided. According to the anchor effect, metal and resin are integrally fixed and formed into one body due to the shrinkage of resin. Mechanical strength provided by the anchor effect is affected by the type of resin, for example, by the rigidity and shrinkage ratio of resin, the profile of the anchor, and the arrangement of the anchor. Therefore, in order to provide the anchor effect, it is necessary to investigate the construction of each product. Accordingly, manufacturing takes a long time. Further, when a molding is formed and cooled, shrinkage is caused in the resin, so that a gap is formed between the metallic parts and the resin. Therefore, not only the appearance of the product deteriorates but also dewing (or wetting) by water vapor condensation tends to occur, which is not preferable for an electronic apparatus casing. Therefore, it is necessary to adhere the metallic parts to the resin.
In order to solve the above problems, according to Japanese Unexamined Patent Publication No. 5-104638, a method of manufacturing a hybrid body of base material and resin is proposed, characterized in that: adhesive is coated on the surface of a metallic base so as to form an adhesive layer; the coated adhesive is hardened; and then, resin is provided on the surface of the hardened adhesive layer so that the metallic base can be integrated with the resin. According to this method, even when the resin is provided on the surface of the adhesive layer at high temperature and pressure, the adhesive layer does not flow out, so that the base and resin can be integrated into one body in a short period of time, and high adhesive force can be obtained.